Laser bond inspection (LBI) may be used for non-destructive inspection of structures assembled with adhesive bonds. LBI typically involves depositing laser energy onto the front surface of a bonded article, thereby generating compression waves that reflect off of a back surface of the bonded article as tensile waves. The tensile waves provide stresses that interrogate the strength or relative quality of a bond.
Similar to LBI is laser induced bond delamination, which generally includes laser processing a bonded structure to intentionally induce defects in one or more bonds contained in the bonded structure.
With reference to FIG. 1, a general LBI and bond delamination process 100 is illustrated. In each of these applications, before laser processing a workpiece, an overlay coating 112, which may be substantially opaque to laser beam 102, may be applied to a front surface 106 of a workpiece being processed. An additional layer 110, which may be substantially transparent to laser beam 102, may be applied over opaque overlay 112, or directly onto workpiece surface 106 (i.e., no opaque overlay coating is applied). Opaque overlay 112 may include, without limitation, tape, paint, or a liquid erosion-resistant coating as described in U.S. Pat. No. 7,268,317, which is incorporated herein by reference in its entirety. Transparent overlay 110 may include, but is not limited to, water, water-based solution, other noncorrosive liquids, glass, sodium silicate, fused silica, potassium chloride, sodium chloride, polyethylene, fluoroplastics, nitrocellulose, and mixtures thereof.
Laser pulse 102 passes through transparent overlay 110 and strikes opaque overlay 112, causing a portion of opaque overlay 112 to vaporize. The vapor absorbs the remaining laser energy and produces a rapidly expanding plasma plume 118. Since expanding plasma 118 is confined momentarily between workpiece surface 106 and transparent overlay 110, a rapidly rising high-pressure shock wave 108 is created which propagates into material 104. Compressive wave 108 propagates through material 104 and may reflect off back surface 116 of material 104 as a tensile wave (not shown) to interrogate bond 114, or may be used to introduce defects into bond 114.
An LBI process often produces debris and effluent backscatter from target sources, contaminating nearby optics such as a final focusing lens, and other optical components of LBI equipment. In some instances, these contaminants accumulate on optical components, such as lenses, during LBI, and absorb laser radiation which may cause damage to optical components. Thus, what is needed is a simple, low-cost solution to protect laser bond inspection optical components.